$4/month for 10 gigs is a nice price point. I sent an email to Dropbox a while ago asking them for something similar, because I didn't need 50 gigs, but 2 wasn't really enough.
I used their 50 gig/6 months promotion a while back, and when it ran out I wasn't using it enough so I thought about cancelling, but the 20 gig option was what saved it for me, which in itself is interesting because the difference is only 3 bucks :-)
Here's a screenshot of dropbox.com/plans for me: http://grab.by/COT